Amazon was expected to account for almost 14% of all online retail sales across the world by the end of 2019, according to Statista. The company rolled out Prime same-day delivery back in 2009 and is currently testing drone delivery, which could mean customers will start to receive their orders in just 30 minutes. But how does Amazon currently get items to you so quickly? We visited one of its fulfilment centres in Tilbury, UK, to learn about the process behind the scenes. All information is as provided to us by Amazon.

Containing 16 miles (25.7km) of conveyor belts, 3,000 robotic units and 2,000 members of staff, Amazon’s fulfilment centre in Tilbury, Essex is one of the largest in Europe. With a convenient location – a one-hour drive from central London – Tilbury Fulfilment Centre is popular for those keen to learn more about the company, and it runs public tours three times a day.

As a visit to the centre makes clear, the journey a product makes from when you click to buy it to the moment when that item actually arrives at your door has many stages. First of all, the item enters the building and is received by a staff member, who will ensure the product has the correct barcode and is in good condition. 

Next, the item is “stowed” in a small tray at random, alongside other items – anything from a camera to a pair of socks to a colouring book – which are stacked up in a shelving unit. At the Tilbury centre, all items are relatively small in size, as larger items are sent to specific fulfilment centres.

The shelving unit is lifted up by a small robotic device, which directs it to the correct place via QR codes – a type of barcode – on the floor. The robot also has cameras that can see above, below and to the sides, so it knows which way to go. It doesn’t work directly with humans – it’s in a fenced-off part of the warehouse for safety reasons. 

The only exception to this rule is the specially-trained workers, who wear red high-vis jackets, can enter the robot zone. Their jackets emit radio signals which tell the robots to move around them, which means that these workers can safely enter the area in order to sort out any technical issues without the risk of a robot driving into them.

Once the robot has stowed the item among other products, it’ll move towards gates – again guided by QR codes on the floor which direct them to the correct workstation – where human employees grab the item from the other side and scan it. From this the worker will know where the item needs to be sent next.

As for stock-taking? It’s all done by artificial intelligence. A machine takes a photograph of each shelving unit which tells it how many of each product are on the shelves. Then the item is sent via conveyor belts – of which there are a staggering 16 miles (25.7km) in this warehouse – and onto the next floor for packing.

Next up…packing. There are different stations for packing multiple and single items. At a single-item station (pictured), the worker receives the item and scans it, which tells them which size of box and packing tape they need to use. It also prints out a unique barcode for the package.

After packaging the item, the correct shelf opposite lights up, telling the employee where it needs to be placed. Additionally, there are lights on top of each packer’s work station. These are lit green if it’s all going smoothly, but the worker can activate them to light orange for a minor issue (such as if they’re running out of packing tape) or red for a more serious issue.

Afterwards, it’s sent along another of the warehouse’s myriad conveyor belts, to the SLAM machine (pictured). The machine – which is an acronym for Scan, Label, Apply, Manifest – scans the unique barcode on each box and applies its shipping label with the address details of the recipient.

Discover how Jeff Bezos went from online bookstore to investing in space travel

The SLAM machine also weighs the parcel to check it matches the expected weight – if it doesn’t, the box is pushed off the conveyor belt and sent off to quality control for further inspection.

Once the shipping label has been applied, the item makes its way to the relevant station for its destination and carrier, where it will end up with other items headed for similar locations.

Finally, the carrier will head out on the road with your item before it’s delivered to your door. Items processed at Tilbury are usually sent to UK locations, but they can end up being sent all across Europe, too.

With robots whizzing about in the warehouse today, it’s easy to imagine that Amazon’s process will be fully automated in a matter of years. But that’s not the case. For one thing, certain tasks require human dexterity and judgement which are incredibly difficult – and expensive – to replace with robots. The technology just doesn’t exist to replicate those features.

It’s also true that in order to have robots you will always need robotics engineers to build, maintain and improve them. These jobs simply wouldn’t have existed twenty years ago. In fact, the increasing number of robots in Amazon warehouses has gone hand-in-hand with an increase in the number of jobs, with Amazon announcing in July 2019 that it was set to create 2,000 new jobs in the UK alone. 

Read more: Strange facts you didn't know about Amazon